The invention relates to the field of carton forming, and more particularly to apparatus for forming and adhesively bonding a carton formed from a coated paperboard blank.
Many types of cartons formed from folded paperboard or the like have been developed over the years. These cartons fall into two major groups, namely cartons which use interlocking corners and tabs to secure the carton in the erected position, and cartons which have an adhesive coating applied to selected portions of the paperboard blank. The latter cartons when erected, are secured in their erected position by the adhesive bond which forms between the panels.
Carton blanks which are to be adhesively bonded generally include at least a base panel, wall panels attached to the base panel, and gussets or panels formed at the corners of the wall panels. Adhesive is coated on the corner panels, or alternatively on portions of the wall panels adjacent the corner panels, and the carton walls and corner panels erected and folded into contact with one another and secured together for a time sufficient to allow the adhesive to set.
Prior art machines for performing such carton forming and gluing operations are exemplified by the patent to Hoyrup, U.S. Pat. No. 3,626,819 issued on Dec. 14, 1971 and assigned to the assignee of the present invention. This patent shows a vertically reciprocating plunger disposed above a carton forming die. A movable carrier having a suction cup transfers the carton blank from a stack into contacting registration with the upper surface of the carton forming die. The die includes a number of vertical posts for controllably erecting and folding wall panels of a carton blank disposed over the die when the carton blank is forced therein by the motion of the plunger. Spots or strips of adhesive are applied to the under surface of the blank at the die mouth by a daubing applicator which rises from a pool of adhesive disposed next to the die. One disadvantage of this prior art type of apparatus is that when a number of spots of adhesive must be applied to a carton blank, such as a clam-shell type blank, the large number of adhesive applicators and associated mechanisms which would be required would interfere with the carton folding process. Also, the daubers are known to have to be cleaned frequently and this adds to the overall costs of the packaging operation.
An alternative method of coating portions of a carton blank with adhesive involves the use of a spring-biased ball dispenser attached to a pivoting arm mounted adjacent the forming head, as shown in the patent to Zanetti, U.S. Pat. No. 1,965,274, issued on June 2, 1917. Adhesive applicators have also been placed on a separate glueing frame which swings across the carton blank before die forming, as shown in U.S. Pat. Application Ser. No. 3,854,385, issued on Nov. 14, 1961.
Finally, the patent to Mosse, U.S. Pat. No. 3,008,386, shows a moving carrier for transferring a carton blank from a stack into registration over a carton forming die in which the carrier includes a resistance heater for activating a thermoplastic adhesive coating applied to portions of the blank.
In order to increase the "throughput", or number of cartons which can be formed and glued within a given amount of time, it would be desirable to provide carton forming apparatus of the type described with some means for accurately and economically applying adhesive to a carton blank which would not interfere in any way with the carton forming apparatus itself. It is desirable to have such adhesive application means light in weight and relatively simple and inexpensive to construct and maintain. It is also desirable that such adhesive application means include some means to prevent application of adhesive when a carton blank is not registered over the mouth of the carton forming die.
It is therefore an object of the invention to provide apparatus for rapidly forming an adhesive bonded carton having improved adhesive application means.
It is another object to provide apparatus for rapidly forming an adhesive bonded carton having adhesive application means attached directly to the carton blank transfer frame.
It is a further object to provide apparatus for rapidly forming an adhesive bonded carton having means for securing the adhesively bonded joints of a carton after forming.
It is yet a further object to provide apparatus for rapidly forming an adhesive bonded carton including means for preventing actuation of the adhesive applicator means when no carton blank is attached to the carton blank transfer frame.
These and other objects are achieved by the present invention wherein there is provided improved apparatus for adhesively bonding a carton. The paperboard clam-shell blank from which the carton is formed includes at least a base panel, wall panels attached to the base panel, and corner panels formed at the corners of the wall panels. The apparatus includes a carton forming die for receiving a paperboard blank, a reciprocating plunger mounted above the die for forcing the carton blank into the die to erect and form the carton, a movable frame having one or more vacuum assisted suction cups mounted thereto for lifting a carton blank from a stack, and means for moving the frame to transfer the carton blank held by the suction cups from the stack into registration over the forming die and for pressing the carton blank into contact with the die. The adhesive applying means includes one or more spring-loaded adhesive applicators connected to a pressurized source of liquid adhesive for applying adhesive to a selected portion of the carton blank when the carton blank is pressed into contacting registration with the die. A stacking cage disposed beneath the carton forming die receives and retains the erected and formed carton in a vertically stacked, nested arrangement, whereby the adhesive coated corners of the carton are retained in contact with adjacent carton wall panels by the pressure applied from the previous nested carton, for a time sufficient to allow an adhesive bond to form therebetween.
The spring-loaded adhesive applicator of the invention, includes a hollow cylindrical feed tube connected to a source of pressurized liquid adhesive, a constricted opening formed in the feed tube, and a spring-biased ball valve disposed in the constricted feed tube opening. When the carton blank, carried by the movable frame, is pressed into contacting registration with the forming die, the spring biased ball valve is displaced by contact with the carton blank and pressurized adhesive flows therethrough onto the carton blank. Openings formed on the surface of the die cooperate with the adhesive applicators when no carton blank is secured to the movable transfer frame. As will be understood more fully below, the carton blank forms a bridge over the openings in order to lift the ball in the valve off the seat thereby providing the desired controlled spot of adhesive.
The adhesive applicators of the present invention are small in size and light in weight, permitting a number of such applicators to be mounted on the carton blank transfer frame without unduly burdening the frame with excessive weight that would otherwise limit speed. These small size applicators can be used in the limited space available on the transfer frames in modern carton folding apparatus with a minimum amount of modification.
The spring-loaded applicators are self-opening when contacting the carton, thus eliminating the need for complex and heavy solenoid or air-actuated adhesive valves. The adhesive applicators accurately dispense the proper amount of liquid adhesive to selected areas of the carton blank with little or no wastage or spilling of adhesive.
The adhesively coated carton is rapidly set up by the reciprocating plunger of the apparatus of the present invention which forces the carton through the die to erect the carton walls and fold the corner panels of the carton into contact with adhesive coated portions of adjacent carton walls. When the reciprocating plunger reaches its lowest point of harmonic motion with respect to the forming die, the erected carton is ejected from the lower portion of the forming die into a stacking cage which retains the cartons in a stacked arrangement. The cartons are nested one above the other to secure the adhesive coated portions of the wall panels against the corner panels for a time sufficient to allow an adhesive bond to form therebetween. Since the adhesive sets while the erected carton is securely retained in the stacking cage by the pressure applied from neighboring nested cartons, the throughput of the carton forming apparatus is independent of the adhesive setting time. Thus, the number of cartons which can be set up and bonded within a given period of time depends mainly on how quickly a carton blank can be fed into the registration with the die and then forced therethrough by the reciprocating plunger.